Filter elements are utilized in a wide variety of applications where it is necessary to remove contaminants, especially particulate dust contaminates, from a fluid stream such as a gaseous or air stream. Typical applications include air filtering of combustion air induction systems of engines for motor vehicles, commercial vehicles, construction and agricultural equipment. Air filters in such services protect the engine components by removing dust contaminants from the air stream. If the air stream is poorly or inadequately filtered, then dust and particulates present in the outside air can penetrate into the engine and to some extent into the engine lubricating oil. In this fashion, particulate dust can accumulate in tight tolerance critical engine areas such as the clearance gaps between the cylinder liners and piston rings where the contaminants eventually cause wear and premature failure of the components.
Axial flow filter elements as primary filters have been developed to provide a very compact filter design having a high filtering surface area in a small component volume. Axial flow filters are applied to filtering applications where their relatively high flow capacity in a small package size and efficient design are beneficial. In applications where the particulate load in the filtered gaseous fluid stream is relatively high or in applications when the filtered gaseous stream contains larger size contaminant particles, then the useful operating life of the filter element may be shortened. Contaminants are trapped in or near the filter media and accumulate over time. If the air stream has a significant particulate contaminant load, then the contaminant load in the filter element can accumulate quickly, resulting in clogging of the filter element and an increase in the pressure drop between the dirty air side and the clean air side of the filter.
U.S. Pat. No. 6,221,122 discloses a filter element designed for use as a secondary filtering element to be installed separately downstream of a primary filtering element. The secondary filtering element serving as a safety filtering element to prevent at least some particles from entering an engine air intake system in the event when the primary filtering device is removed, say for instance when the primary filter is being replaced. As the secondary air filter element is positioned after the primary filter, the secondary air filter is not effective in reducing contaminant fouling of the primary filter.
U.S. Pat. No. 7,115,156 discloses a filter system for filtering intake air for a combustion engine. This patent discloses a housing having an arrangement of filters for filtering air in a serial fashion, including at least one pre-filter, one main or primary filter and one secondary filter.
United States Patent Publication 2007/0271886 discloses a filter element which is formed particularly of a flat element wrapped into a compact body and which along its outer circumference has at least one sealing ring disposed adjacent to the inlet face.
United States Published Patent Application 2002/0150805 discloses a multi-stage filter assembly for removing contaminants from an incoming dirty air stream.
In filtering applications where the particulate load in the filtered gaseous fluid stream is relatively high or in applications when the filtered gaseous stream contains larger size contaminant particles, the useful life of the filter element may be shortened. The dirt load in the filter element accumulates quickly, resulting in clogging of the filter element and an increase in the pressure drop between the dirty air side and the clean air side of the filter. The increasing filter pressure drop soon necessitates the replacement of the filter. Axial flow filters are typically more costly than pleated panel filters, and so improvements that would extend the service life of such filter elements would be novel and useful.